Oxymethylene polymers represent an important class of engineering resins due to numerous favorable physical properties. For this reason, oxymethylene polymers have a wide range of commercial applications, for example, as parts for automobiles, as plumbing components and a variety of household and personal products.
It is oftentimes desireable to modify one or more of the inherently advantageous physical properties of oxymethylene polymers so as to meet the needs of specific end-use applications. Normally, to achieve such modified properties, oxymethylene polymers are usually blended with a variety of other resins and/or ingredients (e.g., impact modifying agents, flame retardants, light and heat stabilizers, fillers, and the like). Usually the blending of property-modifying agents with oxymethylene polymers is not without its own problems due principally to the highly crystalline nature of oxymethylene polymers which is evident in a low level of compatibility with other polymers.
For example, it has been proposed in U.S. Pat. No. 2,993,025 issued to Alsup et al on Jul. 18, 1961 (the entire content of which is expressly incorporated hereinto by reference) to blend superpolyamides with polyoxymethylene so as to provide a composition exhibiting improved thermal stability characteristics. However, when polyamides are blended with oxymethylene polymers, formation of so-called "black specks" usually occurs. To combat the deleterious formation of black specks, it has been suggested to incorporate polyamides having a melting or softening point below that of the oxymethylene polymer by adding the polyamide to the oxymethylene polymer as a dispersion of the polyamide in a carrier resin which is inert to the oxymethylene polymer (see U.S. Pat. No. 4,666,995 issued to Auerbach et al on May 19, 1987, the entire content of which is expressly incorporated hereinto by reference).
Grafting of amine functional polymers onto an oxymethylene backbone would present an attractive alternative to blending so as to achieve a block copolymer having the desired modified properties and/or to employ such a graft copolymer as a compatibilizing agent for compositions containing a blend of oxymethylene polymer and the amine functional polymer per se. However, with oxymethylene polymers, grafting is usually not possible due to the low level of polyacetal end group functionality--that is, since each oxymethylene molecule carries a maximum of two functional groups, e.g., hydroxyl end groups.
According to the present invention, however, grafting of amine functional polymers onto oxymethylene backbones is accomplished by increasing the reactive sites on the oxymethylene polymers. That is, the oxymethylene polymers employed in the present invention will exhibit increased functionality, in the form of reactive pendant groups (e.g., acrylate or substituted acrylate ester groups). Hence, these functionalized oxymethylene polymers may be reacted with suitable amine functional polymers so as to obtain the graft polymers of this invention.
The preferred oxymethylene polymer backbones onto which the amine functional polymers are grafted are essentially random copolymers containing oxymethylene units interspersed with higher oxyalkylene units having pendant acrylate or substituted acrylate ester groups. These pendant functional groups of the higher oxyalkylene units therefore provide reactive sites for the grafting of amine-terminated polymers onto the oxymethylene backbone.
The novel graft polymers of this invention may find usefullness as an engineering resin per se (i.e., resins in which thermal stabilizing agents--the amine functional polymers--are chemically bound to the oxymethylene backbone) and/or as compatibilizing agents so as to compatibilize blends of oxymethylene polymers and the same or chemically similar polymers as are bound to the oxymethylene backbone, and/or as polymer modifiers and additives.
Further aspects and advantages of this invention will become more clear after consideration is given to the following detailed description thereof.